The present invention relates to a means of determining the operating condition of a medical pump. More particularly, this invention relates to a means of determining fluid status in positive displacement fluid pumping devices for the delivery of fluids to a patient.
Modern medical care often involves the use of medical pump devices to deliver fluids and/or fluid medicine to patients. Medical pumps permit the controlled delivery of fluids to a patient, and such pumps have largely replaced gravity flow systems, primarily due to the pump's much greater accuracy in delivery rates and dosages, and due to the possibility for flexible yet controlled delivery schedules. Of the modern medical pumps, those incorporating a diaphragm or pump cassette are often preferred because they provide a more accurate controlled rate and volume than do other types of pumps.
A typical positive displacement pump system includes a pump device driver and a disposable cassette. The disposable cassette, which is adapted to be used only for a single patient and for one fluid delivery cycle, is typically a small plastic unit having an inlet and an outlet respectively connected through flexible tubing to the fluid supply container and to the patient receiving the fluid. The cassette includes a pumping chamber, with the flow of fluid through the chamber being controlled by a plunger or pumping element 38 activated in a controlled manner by the device driver.
For example, the cassette chamber may have one wall formed by a flexible diaphragm which is reciprocated by the plunger and the driver to cause fluid to flow. The pump driver device includes the plunger or pumping element 38 for controlling the flow of fluid into and out of the pumping chamber in the cassette, and it also includes control mechanisms to assure that the fluid is delivered to the patient at a pre-set rate, in a pre-determined manner, and only for a particular pre-selected time or total dosage.
The fluid enters the cassette through an inlet and is forced through an outlet under pressure. The fluid is delivered to the outlet when the pump plunger forces the membrane into the pumping chamber to displace the fluid. During the intake stroke the pump plunger draws back, the membrane covering the pumping chamber pulls back from its prior fully displaced configuration, and the fluid is then drawn through the open inlet and into the pumping chamber. In a pumping stroke, the pump plunger forces the membrane back into the pumping chamber to force the fluid contained therein through the outlet. Thus, the fluid flows from the cassette in a series of spaced-apart pulses rather than in a continuous flow.
One of the requirements for a medical pump is that it is able to detect when it is operating under certain abnormal situations and to alert the user to these problems. Specifically, the pump should detect when flow of fluid is blocked, there is no fluid in the line, there is no cassette in the pump, if the pump has primed correctly, and if the valves in the pump are sealing properly.
Previous pumps that could supply all this information used at least two sensors associated with the pumping chamber or tubes to provide input regarding the fluid conditions to the control system. The use of multiple sensors requires more physical space on the pump and potentially results in a higher unit manufacturing cost.
It is therefore a principal object of this invention to provide means for using a single pressure sensor to discriminate between operating conditions in a medical pump.
These and other objects will be apparent to those skilled in the art.